The present invention relates to grinding machines in general, and more particularly to improvements in grinding machines which can be used for the treatment of workpieces having an at least partially non-circular outline, for example, camshafts for use in the engines of motor vehicles.
A cam grinding machine is disclosed in U.S. Pat. No. 3,344,559 to Seiuemon Inaba et al. The movements of the carriage for the grinding wheel of the patented machine are numerically controlled, i.e., the carriage is automatically moved toward and away from the workpiece in order to enable the working surface of the grinding wheel to adequately treat the entire camshaft including those portions whose radii of curvature are constant as well as those portions which constitute lobes. The carriage for the spindle of the grinding wheel further supports the prime mover which rotates the grinding wheel as well as a dressing apparatus for the working surface of the grinding wheel. Thus, the combined mass of the carriage and of the components which are mounted thereon is very pronounced, and this creates problems when the speed of such machines is to be increased in order to increase their output per unit of time. This is achieved by increasing the speed at which the workpiece is rotated about its axis during treatment by the working surface of the grinding wheel. When the rotational speed of the workpiece reaches a certain value, the characteristic frequency of the control system (which increases with the increasing angular velocity of the workpiece) and the characteristic frequency of the mechanical unit including the carriage and the prime mover for the spindle of the grinding wheel can reach a range of resonances at which the grinding wheel performs uncontrollable vibratory movements. This, in turn, prevents the machine from treating a rapidly rotating camshaft or an analogous workpiece with a required degree of accuracy In addition, and due to relatively large mass of the carriage and of the parts which are mounted thereon, it is necessary to employ extremely accurate controls as well as very rigid and sturdy parts, even at relatively low angular velocities of the workpiece, in order to ensure that the treatment will be carried out with a required degree of accuracy.